// Copyright (c) Google LLC 2019

//

// Use of this source code is governed by an MIT-style

// license that can be found in the LICENSE file or at

// https://opensource.org/licenses/MIT.

// Library to decode the ANS population counts from the bit-stream and build a

// decoding table from them.

#ifndef BRUNSLI_DEC_ANS_DECODE_H_

#define BRUNSLI_DEC_ANS_DECODE_H_

#include <brunsli/types.h>

#include <vector>

#include "../common/ans_params.h"

#include "./brunsli_input.h"

namespace brunsli {

typedef struct {

  uint16_t offset_;

  uint16_t freq_;

  uint8_t symbol_;

} ANSSymbolInfo;

struct ANSDecodingData {

  ANSDecodingData() {}

  bool Init(const std::vector<uint32_t>& counts);

  ANSSymbolInfo map_[BRUNSLI_ANS_TAB_SIZE];

};

class ANSDecoder {

 public:

  ANSDecoder() {}

  void Init(WordSource* in) {

    state_ = in->GetNextWord();

    state_ = (state_ << 16u) | in->GetNextWord();

  }

  int ReadSymbol(const ANSDecodingData& code, WordSource* in) {

    const uint32_t res = state_ & (BRUNSLI_ANS_TAB_SIZE - 1);

    const ANSSymbolInfo& s = code.map_[res];

    state_ = s.freq_ * (state_ >> BRUNSLI_ANS_LOG_TAB_SIZE) + s.offset_;

    if (state_ < (1u << 16u)) {

      state_ = (state_ << 16u) | in->GetNextWord();

    }

    return s.symbol_;

  }

  bool CheckCRC() const { return state_ == (BRUNSLI_ANS_SIGNATURE << 16u); }

 private:

  uint32_t state_;

};

}  // namespace brunsli

#endif  // BRUNSLI_DEC_ANS_DECODE_H_